A number of banknote handling apparatuses, such as banknote validators, stackers for use in conjunction with banknote validators and combined validator and stacker units are presently known including the validator described in U.S. Pat. No. 4,628,194 issued on Dec. 9, 1986 and the stackers described in U.S. application Ser. Nos. 709,559 and 904,714 filed on Mar. 8, 1985 and Sept. 5, 1986 respectively. Each of the above identified applications is assigned to the assignee of the present application. In the banknote stackers, a fixed braking time is used to insure that the stacker pusher motor is properly stopped in its home position. Also, the final location of a banknote to be stacked is determined by driving the banknote transporting apparatus and consequently the banknote a fixed time from its exit from the validator portion of the banknote handling apparatus, and allowing the banknote to coast to a stop. Alternatively, a fixed brake time might have been used to stop the banknote just as a fixed brake time was applied to stop the pusher motor. During the fixed brake time for the pusher motor, a reverse drive signal is applied in order to bring the pusher motor to a stop. With the application of a fixed brake time, variations in the final stop position may occur. Similarly, if a fixed brake time is applied to the banknote transporting apparatus, variations in the final stop position of the banknote may occur, depending on banknote speed. For example, if the banknote is traveling too rapidly, a fixed braking time will not be sufficient and the banknote will overshoot its intended stop position. If the banknote is traveling too slowly, a fixed braking time will be too long and the braking operation will result in the banknote being driven backwards so that it is stopped at a position before the correct stop position, thereby undershooting the proper stop position.
Such speed variations can occur as a result of the differences between crisp, new banknotes and worn, old banknotes, component aging, product environmental changes, and the like. Additionally, as the beginning of the drive time is based on the release of a jam sensor or other mechanical switch, the variations in the response time of the mechanical switch affects the final position of the bill.
Other schemes have been used to determine the position of a banknote in a stacker housing. These schemes include using actual feedback from drive motor arrangement employing a decoder circuit to determine the actual distance the banknote has been driven based upon a calculation of the number of rotations of the drive motor. This arrangement accounts for speed variations of the drive motor, but not for slippage of the banknote. Additionally, the problems recited above associated with applying fixed brake times are also present for this arrangement. More complicated arrangements employing a number of position sensing switches are also known.